Various conditions, e.g., age-related macular degeneration, retinitis pigmentosa, etc., exist which effect the functioning of photoreceptors (i.e., rods and cones) on a patient's retina and thus eliminate or severely degrade the patient's vision. To overcome these conditions, it has been proposed to directly stimulate the visual cortex (see for example, Bindley G, Lewin W. The sensations produced by electrical stimulation of the visual cortex. J. Physiol (London) 1968:196:479-493) or to implant a retinal prosthesis to stimulate neural pathways within a patient's retina (see for example, U.S. Pat. No. 4,628,933 to Michelson and U.S. Pat. No. 5,935,155 to Humayun et al.). Each of these approaches potentially suffer from resolution problems in that the various mechanical, electromechanical, thermal and other technological limitations may, within the foreseeable future, significantly limit the resolution of an image that can be imparted to the patient's brain. For example, while a normal retina's resolution may be in the order of 4,000,000 pixels (picture elements), and the resolution of a computer screen (or compatible charge-coupled device (CCD) video camera) is of the order of 1,000,000 pixels, a reasonable goal for the aforementioned technologies may be 1,000 pixels. Accordingly, the visual acuity would potentially be degraded by a factor of at least 1,000 (still a significant benefit for patients in need of such devices). In some of the aforementioned devices, e.g., the Michelson device, there is a direct one-to-one relationship between each video processing component, e.g., CCD element, and the electrode that stimulates the retina (see FIG. 6), while in other devices, e.g., the Humayun et al. device, this relationship is not expressly discussed.
Additionally, it has been observed that normal eyes periodically jitter, i.e., they are subject to fast movements of the eyes separated by fixation periods during which the eyes are relatively still. While such eye movements (also referred to as saccadic eye movements) may represent vestigial physiological features that are overcome by processing in the patient's brain, some people believe that this saccadic movement actually increases the perceived resolution of the visual image beyond that which could otherwise be achieved solely based on the retinal photoreceptor density.
Accordingly, what is needed are techniques and apparatus for applying such techniques that can obtain the benefits of a “high” resolution video device/signal and process such signal to enhance the perceived visual acuity beyond that of a “low” resolution electrode array.